1. Field of the Invention
The present invention relates to a vehicle control device for enabling an driver of a vehicle to surely recognize that air pressure of a tire is reduced to predetermined pressure or less when the air pressure of the tire is reduced to the predetermined pressure or less.
2. Description of the Related Art
When the air pressure of a tire is gradually reduced during traveling of a vehicle, a driver hardly recognizes reduction in air pressure because he/she does not immediately have uncomfortable feeling. However, the reduction in air pressure causes tire burst or the like, and has risky elements such as induction of abnormality in a steering operation at a curve, etc., so that it is necessary to inform the reduction of air pressure to a driver. Accordingly, there has been proposed a vehicle equipped with a tire air pressure alarming device in which the air pressure of a tire (tires) is directly or indirectly measured and an alarm is emitted by some method to inform reduction in tire air pressure to a driver when the tire air pressure thus measured is reduced to predetermined pressure or less.
For example, JP-A-2002-317679 (hereinafter referred to as Patent Document 1) has proposed a method of restricting the speed of a vehicle when tire air pressure is reduced, thereby enhancing safety of the vehicle.
Furthermore, there has been developed run flat tires with which a vehicle can travel by a predetermined distance if the vehicle speed is equal to a predetermined speed or less even when the tire blows out.
Still furthermore, when the air pressure of a tire at one side of a vehicle is reduced, a driver has an uncomfortable feeling. From this viewpoint, JP-A-2003-220962 (hereinafter referred to as Patent Document 2) has proposed a technique of preventing a driver to have an uncomfortable feeling by changing control characteristics of power steering and vehicle stability control.
Still furthermore, JP-A-2001-80436 (hereinafter referred to as Patent Document 3) has proposed a method of mounting a fluid-filled deformable container of rubber or the like on a site coming into contact with a driver such as a steering wheel and varying the state of the fluid to change a sense of touch when the tire air pressure is reduced, thereby making the driver recognize the reduction in the tire air pressure.
Furthermore, JP-A-2003-25816 (hereinafter referred to as Patent Document 4) has proposed a method of giving minute vibration to a steering system of a lane keep system for making the travel locus of a vehicle follow a target locus through automatic steering control when tire air pressure is reduced, by using an actuator equipped in the steering system, thereby making a driver have a uncomfortable feeling and thus recognize the reduction in tire air pressure.
Even when a tire blows out and an alarm is emitted by a buzzer (alarm sound), there is a probability that a driver cannot perceive the alarm emitted from the buzzer if he/she listens to music or has a conversation with another driver while a vehicle travels. Furthermore, even when an alarm is displayed with a character indication, the driver may pass over the alarm display.
Furthermore, there is a risk that the driver cannot recognize what the alarm means even when the driver perceives or sees the display because blowout of a tire is rare.
The method of restricting the vehicle speed has a problem that a driver does not perceive blowout of a tire with high probability when the vehicle travels at a restricted speed or less.
Furthermore, according to the method using run flat tires, the driver hardly perceives the blowout because the vehicle can travel at a predetermined vehicle speed or less by a predetermined distance after the blowout. Even when the driver perceives the blowout, he/she may continue to drive at a speed exceeding the predetermined speed by a distance exceeding the predetermined distance because he/she is overconfident to the performance of the run flat tires. If the driver does not make any adjustment even when tire air pressure is reduced or the driver does not exchange a blowout tire by a new tire, the control characteristic of the vehicle is varied and thus stability may be lost. Furthermore, the same risk may occur when the vehicle is used under conditions exceeding a predetermined speed and a predetermined distance which are prescribed in the specification of the run flat tires.
In the case of the technique of preventing a driver from having a uncomfortable feeling when a tire blows out, the driver is more and more forgetting to recognize necessity of exchanging a blowout tire, and thus there is a risk that the driver continues to drive the vehicle.
On the other hand, the method of making a driver uncomfortable when tire air pressure is reduced, and thus making the driver recognize the reduction of the tire air pressure has a problem that a device for applying a minute vibration to a steering is newly required and thus the cost is increased.
As described above, all the prior arts have some problems, and there has not been achieved any satisfiable technique.